1. Field of the Invention
The present invention relates to an image forming apparatus including a reconstruction processing portion.
2. Description of the Related Art
There is need for image forming apparatuses employing a toner system to reduce toner consumption in image formation in order to realize low running cost. To that end, Japanese Patent Application Laid-Open No. H08-044178 discloses a method of using a low toner consumption mode in the image forming apparatus of an electrophotographic system. By using the low toner consumption mode disclosed in Japanese Patent Application Laid-Open No. H08-044178, it is possible to realize a reduction in the toner consumption in the image formation.
An image formed in the low toner consumption mode has a low density. When a recording medium on which the image having a normal density is formed is desired, if there is no image data having a normal density, it is conceivable to temporarily read the image formed in the low toner consumption mode from an original to generate image data and to increase a density of the generated image data to form an image on a recording medium with a higher density. However, with this method, a user does not know to which extent to increase the density of the generated image data, and hence it is normally difficult to output an image with a desired normal density with one processing. In that case, it is necessary to repeatedly output an image.
Further, in a case where the image is read by a scanner from the original and the read image data is output to a new recording medium at the density adjusted, the image quality deteriorates in general. In the first place, an S/N ratio of the image data generated by reading the original by the scanner deteriorates compared to an S/N ratio of the image on the original. In this case, representative noise includes a micro-level uneven density caused by uneven transferability due to low smoothness of paper of the original. In addition, when the density of the image is increased, the uneven density also becomes high, with the result that the uneven density becomes more conspicuous.
Here, the uneven density of the image ascribable to the smoothness of the paper can be indicated by an uneven density index. In this case, the uneven density index is defined by scanning by the scanner a paper sheet on which a blue image is formed and obtaining a standard deviation of the square of a reflection density with respect to a basis weight. Assuming that the reflection density is Dr and the basis weight (g/m2) is B, an uneven density index M is a function of (standard deviation of Dr2)/B. Further, as described later, the uneven density index M also changes based on a texture index. It is assumed that the density and the uneven density index of the image of the original are d0 and M0, respectively, and the density and the uneven density index of the image formed on a new recording medium are d1 and Mc, respectively. The uneven density index Mc of the image formed on the recording medium is expressed as Mc=M0×a0 by using density ratio a0 (a0=d1/d0) of the density d1 of the image on the recording medium with respect to the density d0 of the image of the original. In other words, when the density is increased a0-fold, the uneven density index is increased a0-fold as well. FIG. 12 shows the uneven density index Mc with respect to the density ratio a0. As shown in FIG. 12, as the density ratio a0 increases, the uneven density index Mc increases.
As described above, it is difficult to form the image having a desired density on the recording medium with one processing by using the image data generated by reading the image from the original on which the image is formed in the low toner consumption mode. Further, the uneven density increases when the density of the image data is increased.